Provided is a water purification device (100) in which a flow path (40) comprises an inlet (42) and an outlet (44) for water. A light source (30) irradiates water that flows through the flow path (40) with ultraviolet light. The light source (30) comprises a light-emitting diode that emits ultraviolet light having a wavelength that is included in a bandwidth of at least 220 nm and less than 300 nm. The optical output in the wavelength bandwidth is 1-50W. Water passes through the flow path (40) at a flow rate of 5-250 mL per second. The flow path (40) is formed from a wall surface having a tubular shape. A window section (26) through which ultraviolet light is transmitted is provided to at least one part of the wall surface. The light source (30) is provided to a position that corresponds to the window section (26). A reflective section (28) that reflects ultraviolet light is provided to at least one part of the wall surface.